The present invention relates to a solar windshield system comprising three transition lens materials, each transition lens material having a particular darkening strength when exposed to ultraviolet light. More particularly, the present invention relates to a solar windshield system for a vehicle, such as an automobile, having a front windshield composed of a first transition lens material, at least one side window composed of a second transition lens material and a rear windshield composed of a third transition lens material.
Windshield systems for vehicles have undergone numerous modifications throughout the years in order to facilitate driving under various conditions. Reducing the transmission of visible light is one such modification. Many attempts have been made in the prior art to reduce glare, transmission of ultraviolet (UV) light and infrared (IR) light. One type of modification is to tint or glaze the windshield with a compound or film which permanently darkens the windshield. However, a permanent darkening of the windshield hinders driving, particularly at night or during very cloudy and stormy conditions. Another type of xe2x80x9ctintingxe2x80x9d modification is to darken only a portion of the windshield, such as the uppermost portion of the windshield or the periphery of the windshield. For example, U.S. Pat. No. 4,874,654 to Funaki et al., issued Oct. 17, 1989, teaches a vehicle window glass composed of a transparent part and a colored part formed on the periphery of the transparent part. However, an inherent drawback to Funaki et al. is that part of the windshield is permanently darkened while another part is permanently untreated; the untreated portion still being fully exposed to UV and IR light.
Another modification to vehicle windshields is providing a laminated windshield having one layer that is reactive to UV light. For instance, U.S. Pat. No. 4,973,511 to Farmer et al., issued Nov. 27, 1990, provides a laminated window construction comprising a solar control film formed by a flexible plastic substrate having on one surface a multilayer solar coating which provides about 70% normal visible light transmissibility. A drawback to the Farmer et al. window assembly is that the coating provides a permanently 70% transmissibility, even under night time conditions. U.S. Pat. No. 5,956,175 to Hojnowski, issued Sep. 21, 1999, teaches a solar control window film which having high visible light transmission and low transmission of near infrared heat energy. Hojnowski provides a multilayer window having one or more layers which absorb near infrared light and at least one window film having a visible light transmission of about 50 to 80%. However, the window film permanently reduces visible light transmission.
The use of a transition lens material in glasses and windows has been explored. Typically, a transition glass contains millions of photochromic molecules which absorb UV light. When exposed to sunlight (i.e. UV rays), a chemical reaction occurs which transforms the photochromic molecules into colored light absorbers. In other words, exposure to sunlight will activate the photochromic molecules, thereby darkening a transition glass. The absence of sunlight will deactivate the photochromic molecules and the transition glass will revert to its clear state. The degree of darkening, or darkening strength, will depend upon the amount of photochromic material within the transition glass and the intensity of the UV light. Glass photochromic lenses have been available since the 1960""s and plastic photochromic lenses were introduced in the early 1990""s. A conventional glass photochromic lens is the PHOTOGRAY EXTRA(trademark), available from Corning Glass Works, which darkens to 22% transmission in sunlight. Another typical photochromic lens is the PHOTOBROWN EXTRA(trademark), also available from Corning Glass Works.
Examples of windows and vehicle windshields having a photochromic component are known in the art. For instance, U.S. Pat. No. 3,964,823 to Trozollo, issued Jun. 22, 1976, the disclosure of which is incorporated by reference, and U.S. Pat. No. 3,984,177 to Trozzolo, issued Oct. 5, 1976, broadly teach the use of a certain class of photochromic materials in articles such as windshields and glass panes and sunglasses. U.S. Pat. No. 5,390,045 to Bernard, Jr., issued Feb. 14, 1995, teaches an adjustable window tinting system for limiting passage of both visible light and radiative heat, using a glass assembly comprising a photochromatic glass, an electrochromatic glass and a pair of spaced glass pane filled with a tinted fluid. U.S. Pat. No. 6,039,390 to Agrawal et al., issued Mar. 21, 2000, discloses a chromogenic window assembly panel which is composed of several panels, one of which may be a photochromic panel. U.S. Pat. No. 6,094,290 to Crawford et al., issued Jul. 25, 2000, provides a light-reactive thermal window having external and internal panes, the external pane being composed of a photochromic lens material. However, each of these windshield assemblies discloses a construction which is complicated and typically comprising multiple layers.
Although there have been advances in the art with respect to glass assemblies having a photochromic material for utilization as a front windshield, none of prior art discloses or suggests a solar windshield system composed of transition lens materials of varying degrees of darkening strength for use in a vehicles front windshield, rear windshield and side windows. Accordingly, a need still exists for a solar windshield system which utilizes multiple transition lens materials. Such a solar windshield system should provide a first transition lens material having a first darkening strength, a second transition lens material having a second darkening strength which is greater than the first darkening strength and a third transition lens material having a third darkening strength which is greater than the second darkening strength. Such a solar windshield system should utilize the first transition lens material for the front windshield, the second transition lens material for the side windows and the third transition lens material for the rear windshield. Such as solar windshield system should be simple and effective to use and should darken or lighten depending on the degree of exposure to the sun. In addition, such a solar windshield system also should facilitate driving a vehicle when the sunlight is strong and should not diminish driving during the night or at other times when the sunlight is weak. Moreover, such a system should also prevent the interior of a vehicle from becoming heated when exposed to strong sunlight, as well as preserving the vehicle""s interior from damage.
Accordingly, it is an object of the present invention to provide a solar windshield system comprising a first transition lens material having a first darkening strength, a second transition lens material having a second darkening strength which is greater than the first darkening strength an a third transition lens material having a third darkening strength which is greater than the second darkening strength.
It is also an object of the present invention to provide a solar windshield system for a vehicle comprising a front windshield composed of a first transition lens material having a first darkening strength, at least one side window composed of a second transition lens material having a second darkening strength which is greater than the first darkening strength, and a rear windshield composed of a third transition lens material having a third darkening strength which is greater than the second darkening strength.
It is another object of the present invention to provide a solar windshield system wherein the first, second and third transition lens materials are photochromic lens materials.
It is an additional object of the present invention to provide a solar windshield system which is simple and effective to use and which darkens or lightens depending upon the exposure of sunlight.
It is yet another object of the present invention to provide a solar windshield system which facilitates driving a vehicle when the sunlight is strong and which does not diminish driving during the night or at other times when the sunlight is weak.
It is still another object of the present invention to provide a solar windshield system which prevents the interior of a vehicle from becoming heated and/or damaged when exposed to strong sunlight.
Additional objects, advantages and novel features of the invention will be set forth in part of the description and claims which follows, and in part will become apparent to those skilled in the art upon examination of the following specification or may be learned by practice of the invention.